A conventional can body maker apparatus is disclosed in U.S. Pat. No. 3,696,659, issued to J. H. Maytag and assigned to Adolph Coors Company. The contents of this patent are incorporated herein by reference as if fully set forth herein. An example of a conventional redraw system is disclosed in U.S. Pat. No. 3,735,629, issued to Elpidofor Paramonoff, and assigned to Standun Inc., also incorporated by reference as if fully set forth. The assignee of the instant invention is also the assignee of copending application, "Improved Body Maker Apparatus," Serial No. 899,201, which discloses a counterbalance mass system that improves the speed and efficiency of can body makers.
Can body makers produce elongated can bodies from shallow metal cups or can shells. The can shells have a wall thickness of approximately 0.009 to 0.012 inch, and the elongated can bodies have a wall thickness reduced to approximately 0.0045 inch. In a conventional can body maker apparatus, a ram is movably mounted for reciprocal, straight line motion at rates typically sufficient to form from between 180 and 220 can bodies per minute. The stroke length, that is the distance traveled by the movable ram, is between about 18 to 26 inches. As a general rule, for a given can body maker, the shorter the ram stroke, the greater the rate or number of cycles per minute at which the ram can be operated. Misalignment as small as between about 0.0005 and 0.0010 inch can result in the formation of defective cans. In conjunction with the reciprocal motion of the ram, a redraw sleeve is supported in a redraw assembly. The redraw sleeve engages the shell prior to contact by the ram, and applies a restraining force against the shell as the shell is worked through a redraw die. The redraw process elongates the sidewalls of the can shell and decreases the sidewall thickness and overall diameter of the can shell. The redraw operation is followed by two or three ironing stations that further elongate and thin the walls of the can shell to form a one piece can body. The body maker typically includes a doming station that further forms the enclosed bottom of the can body into a desired structural configuration.
The redraw assembly operates at the same rate as the ram assembly. Mechanical linkage is provided between the main crank shaft of the can body maker and both the ram assembly and the redraw assembly. Needless to say, a significant amount of mass is being reciprocated in the redraw carriage assembly and this mass can contribute to the misalignment problem discussed above. Heretofore, it had been the practice to provide a redraw sleeve with an internal bore of a constant diameter. The ram passes through the bore of the sleeve. The bore is of sufficient diameter to relative to the outside diameter of the ram to provide clearance as the ram passes through the bore of the sleeve. The shell contacting surface in such conventional redraw sleeves is the terminal portion of the thick walled sleeve, i.e., the forward portion of the sleeve between its inner and outer cylindrical surfaces. Such conventional redraw sleeves possess significant mass and are subject to minor misalignment during the initial moments of the redraw process. During the redraw process, the redraw sleeve can maintain a pressure of approximately 1,700 pounds of pressure on the can shell. Too little pressure will result in wrinkling, too much pressure will permit the ram to tear through the shell. The redraw sleeve must apply uniform pressure against the shell or the redrawn workpiece will be irregular in appearance and non uniform in thickness and dimension.